1. Field of the Invention
The present invention relates to a zoom lens system and an electronic imaging apparatus using the zoom lens system.
2. Description of Related Art
In recent years there has been an increasing need for a zoom lens system in an electronic imaging apparatus, such as a digital camera, etc., to be more compact (miniaturized) and to have higher optical performance.
Japanese Unexamined Patent Publication Nos. H06-51202, 2002-162564 and 2009-288619 disclose a zoom lens system configured of a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, in that order from the object side.
In each of the zoom lens systems disclosed in these Japanese Unexamined Patent Publications, the number of lens elements to be used for the entire lens system (especially, for the fourth lens group) is too many, and accordingly such zoom lens systems do not sufficiently reduce the weight the zoom lens system. Moreover, the balance of refractive power over the first lens group to the fourth lens group (in particular, the refractive-power balance between the first lens group and the fourth lens group, the refractive-power balance between the second lens group and the third lens group, and the refractive-power balance between the third lens group and the fourth lens group) are not set adequately. Accordingly, aberrations such as field curvature, astigmatism, distortion, spherical aberration and coma, are not sufficiently corrected, which causes deterioration of the optical performance.